Some Info On DMX...Myth?

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ahoustondj

Mac Daddy DJ
Aug 13, 2007
20,235
3,465
Texas
This is an excerpt from an article published by a retailer about myths between Microphone & DMX Cables.

Let's talk about DMX cables... I recently received and email from a blog monitor that said... "There are MICROPHONE cables and there are DMX cables and one can NOT be used for the other". That's a very strong statement. Very "Black and White". Unfortunately, it's also very untrue. That statement would be like saying that Chevy's are for taking your kids to school and Ferrari's are for racing and one can not be used for the other. I have seen many people race Chevy's successfully and I have also seen a few Ferrari's in the school pick up lanes. I don't know exactly why people make those black and white statements about DMX cables. Perhaps they merely lack real world experience in the field. If they had real world experience, they would know that there were companies like NSI making digitally controlled lighting boards and dimmer packs with signals carried thru 3 pin XLR cables long before the term DMX was ever heard of here in America. (NSI calls their proprietary signal MICROPLEX and they still use it today). What do you think those digital signals were carried thru back before the late 90's when DMX was introduced to the commercial market here in America? MICROPHONE CABLES. That's all we had back then, that's what was used and that's what worked for years. Perhaps some cables marked "DMX Cable" might perform better than some cables marked "MICROPHONE Cable", but it can also be proven that some mid to high grade MIC cables work better than some DMX cables and if you and your audience can't tell the difference, who cares? What does matter is which pins the wires are connected to on the 3 pin XLR plug. At High Energy Lighting (CheapLights.com), we currently buy "MIC" cables and "DMX" cables from over 22 different suppliers. Regardless of how they are marked, we test samples from each different "MIC" and "DMX" cable model to make sure they work in a DMX chain before we ever offer them to our customers. Here's an interesting fact... In the ten to fifteen years that we have been selling cables for transmitting digital signals for light processors, we have never had any cables returned by customers saying they didn't work as a DMX cable, unless the cable actually had a physical defect, such as a wire not connected to the plug or a cut in the wire. That's a great statement to be able to make! Here's a few more interesting facts... 1. "DMX" was created in 1986, but not widely used or known. At that time, the popular method for transmitting signal to dimmer packs was zero to ten volts. 2. "DMX" was revised in a major way and started gaining recognition in 1990. (But not in America). 3. The first DMX lighting controllers were displayed at the American LDI Lighting convention in 1999 by LitePuter. 4. "DMX" was introduced as the "Standard" digital signal for the World Wide lighting industry in 2000.
 
Yep... I actually addressed that VERY quote here:

Our DJ Talk - DJ Help and Resources Chat! - View Single Post - DMX cables.. connecting 2 +?

There is a lot of misinformation out there.

Statements like this are not only patently false, but self-serving (like why did they sell you mic cables instead of DMX cables? Did they not have DMX cables on hand?? Do they have a higher margin on mic cables?), but I think they also border on fraud. Will they replace your lighting if it is damaged by the use of poorly shielded cable?

The above statement that was found on another gear resellers site was debated on a "nerd forum" I visit. Some of the replies were as follows:

“I...just...wow…”

“Don't believe everything you read on the Internet, kids.”

“and again..... wow I need to forward this to a friend....wow”

“WHAT?!? It's not just wrong, it's wrong in VERY strange ways. “

and my favorite response was this one:

"I cannot find one statement in this post that is correct. I recommend ignoring it. Unfortunately, I do not have the time or energy to correct each of the multitude of egregious errors"

That was posted by Steve Terry--Chair, USITT Dimmer Standards Committee (authors of the 1986 and 1990 DMX512 standards)--Founding Co-Chair, ESTA Control Protocols Working Group (authors of ANSI E.11-2004 and E1.11-2008, USITT DMX-512A standard)

So don't take my word for it... take Steve's.

Ben
 
Misinformation said:
If they had real world experience, they would know that there were companies like NSI making digitally controlled lighting boards and dimmer packs with signals carried thru 3 pin XLR cables long before the term DMX was ever heard of here in America. (NSI calls their proprietary signal MICROPLEX and they still use it today). What do you think those digital signals were carried thru back before the late 90's when DMX was introduced to the commercial market here in America?

Microplex is actually an analog signal that uses a 12 volt sync pulse and a 0 to +10 volt range for the analog levels. Considering that DMX requires only 200mV to declare a change in state between the DIGITAL values of 1 and 0, that's a pretty poor justification of how Microplex working on microphone cable means that DMX should. I would say that it is just my opinion, but it's not. It's an opinion that is substantiated by scientific, physical fact, and an opinion that is shared by hundreds of immensely qualified people.

Ben
 
Just for the heck of it said:
Regardless of how they are marked, we test samples from each different "MIC" and "DMX" cable model to make sure they work in a DMX chain before we ever offer them to our customers.

Ok... my inner (and outer) nerd is getting pretty riled up here. LOL. I have successfully passed DMX over electric fence cable, and I bet I could do it with a coathanger, and a few other devices. So, using this justification does that mean I should be allowed to sell these as worthy of "DMX" connectivity?

I'm gonna take a deep breath now... and go get some lunch. LOL

Ben
 
This was already addressed in the other thread.

But hey... let's do something else.... You see, the requirement for DMX is based on a standard with impedance equaling 120 Ohm. That requires 120 Ohm cable for BEST PERFORMANCE.

This means that electrically, the signal might work for short distances, when you increase the length, it can (and likely will) fail.

Microphone cables provide a different load than the DMX cables.

Would you take an amplifier that's rated at 4 Ohm stable and run it at 2 Ohms? Not if you want it to keep working. What about 16 Ohm? 32 Ohm? 64 Ohm? 1000 Ohm?

It 'might' work - but it's not the 'best practices' and as you approach the limits of the standard it can and will fail.

If I'm doing uplighting around a 50x50 room - and running from my console on one side (without a 'splitter') - the run will be approx. 200 feet. Would I trust that to a microphone cable? No. Would I do it without a terminator? No. Could I do it with microphone cable and without a terminator? Perhaps. And it might work.... but using the right cables means you KNOW it will work.

If I was doing 2 par cans at my console with a short run between - maybe 15-20 feet - would I use a microphone cable? Sure - I could probably get by with it and it would work just fine.

But let me put it the most simple way I can think of doing it....

Is your reputation worth saving a couple dollars on cabling? batteries? or something else?

Get the right tool for the job and the job is easier...